A helicopter is conventionally provided with a rotary wing for providing it with lift and propulsion. Furthermore, a helicopter sometimes includes an anti-torque tail rotor for countering the torque exerted by the rotary wing on the fuselage of the helicopter.
In order to drive the rotary wing, and where appropriate the anti-torque rotor, the helicopter has a power plant.
The power plant implements one or more engines. It should be understood that throughout this specification, the term “engine” applies equally well to turbine engines or to piston engines. The term “engine” is to be contrasted with the term “electric motor”, where the term “electric motor” designates a motor driven by electricity, a so-called “brushless” motor for example.
Amongst rotorcraft, there are thus so-called “single-engined” helicopters having a power plant that has only one engine in order to drive the rotary wing, and the anti-torque rotor, if any. Conversely, certain helicopters possess at least two engines for this purpose.
It can be understood that single-engined helicopters present advantages that are not negligible compared with helicopters having a plurality of engines. By way of example, mention can be made of cost that is reasonable, of reduced maintenance operations, and of fuel consumption that is relatively low.
Nevertheless, such single-engined helicopters also present drawbacks.
In the event of failures in the single engine of the power plant of a single-engined helicopter, the power plant presents degraded performance. Under extreme circumstances, the power plant is no longer capable of driving the rotary wing and the anti-torque rotor, which is likely to give rise to a situation that is catastrophic.
Under such conditions, the flight domain and the missions that are authorized for single-engined helicopters are kept small by certification authorities that deliver flight authorizations. In particular, overflying a large city in a single-engined helicopter is not allowed, e.g. overlying the capital of France.